Murphy said the SNP would have to decide if they wanted to back Labour legislation but promised: “They vote for it, they vote for it. They vote against it, they would have to live with the consequences of bringing down a Labour government.

“Bring down another Labour government and Scotland will never forgive them. So, no formal coalition.

“If the SNP want to vote for our programme, that’s up to them. And if they want to bring down a Labour government, they’ve done it once before – I wouldn’t put it past them.

“But they paid the price for many years. They say it was an accident. If they do it again, it becomes a habit. The 1979 accident becomes a twice-repeated habit.”

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Miliband is due to arrive in Scotland tomorrow when he will address party activists in a speech in Clydebank. He is expected to tell them that the eyes of Britain will be on Scotland on May 7.

He said: “For the second time in less than a year, the future of the UK lies in the hands of people in Scotland.

“The responsibility couldn’t be greater because it’s the votes of people in Scotland that will determine whether we get a Labour government on the side of working families or a Tory decade of austerity.

“It’s a straight choice between a Labour government that will make it worth people’s while going out to work each day or a Tory government that will put the funding for Scotland’s NHS at risk. Scotland needs a Labour government to give young people in Scotland a chance of a better future.”

But SNP deputy leader Stewart Hosie said: “If there are more anti-Tory MPs than Tory MPs, the SNP and Labour combined can lock David Cameron out of Downing Street.

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“The people of Scotland would never forget or forgive Labour if they let the Tories back into government in preference to working with the SNP.”

Meanwhile, the UK Government’s legislative response to the Smith Commission on more powers for Scotland falls far short of being a credible bill, a committee of MPs has concluded.

Question -1 of 5Score -0 of 0

What were little Ariana Sufi's first words that she muttered when she was 7 weeks old?